Interpretive Summary: Progesterone plays important roles in normal development and cancer, and it controls specific processes depending on the type of cell it targets. Here, we demonstrated the involvement of a protein called BTEB1 in controlling the action of progesterone in the uterus; hence, contributing to a better understanding of the mechanism involved in normal and tumor development of the uterus.

Technical Abstract:
Progesterone receptor (PR), a ligand-inducible transcription factor mediates the physiological actions of progesterone (P) through two distinct isoforms PR-A and PR-B and numerous nuclear factors. We demonstrated previously that basic transcription element-binding protein-1 (BTEB1), a transcription factor belonging to the Krüppel-like family, is a functional PR-interacting protein, based on the sub-fertility phenotype and reduced P-sensitivity of uterine PR target genes, upon BTEB1 null mutation. Here, we examined the role of BTEB1 in PR-mediated signaling in uterine endometrial epithelial cells using the human endocarcinoma cell line Ishikawa and the epithelial-expressed, P-responsive secretory leukocyte protease inhibitor (SLPI) gene. Treatment of Ishikawa cells with P increased SLPI and BTEB1 transcript levels without similar effects on total PR-A/B and PR-B expression. P-induction was abolished by the PR antagonist RU486, while knockdown of BTEB1 with short interfering RNA reduced P-responsive BTEB1 but not SLPI expression to basal levels. Forced expression of BTEB1, either by stable (Hec1A) or transient (Ishikawa) transfections of BTEB1 expression constructs, enhanced SLPI promoter activity. Chromatin immunoprecipitation demonstrated BTEB1 recruitment to the proximal GC-rich containing (-97 to -86) SLPI promoter region in BTEB1 over-expressing Hec-1A cells. In Ishikawa cells, recruitment of BTEB1 to the proximal, GC-rich region as well as to a distal, PRE-like containing (-635 to -514) region was P-dependent and was accompanied by co-recruitment of PR and the PR coactivator CBP. Association of BTEB1 was preferential to the PR-B isoform in the GC-rich region, whereas both PR isoforms were recruited to the PRE-like site along with BTEB1. Our findings define a novel pathway for BTEB1/PR cross-talk to facilitate P-dependent gene transcription in endometrial epithelial cells.